For example, JP-2004-106778-A discloses a reservoir tank is used for a master cylinder unit or a hydraulic control unit for a motor vehicle.
When used for a master cylinder unit, a reservoir tank is configured as a separate tank from the master cylinder unit, which supplies a hydraulic fluid to the master cylinder unit via a connecting hose or the like.
In the reservoir tank in JP-2004-106778-A, a filter is attached to a pouring port of a hydraulic fluid. In this reservoir tank, however, once foreign matters such as dust are allowed to enter the tank while the tank is maintained regularly as when filters are replaced, it has been difficult to trap the foreign matters in the tank.